At last, we are finally ready to build the “heart of the MST-13” timer. You certainly remember that we have the circuit diagram designed by Lumpert.
And this is the part that we will focus on.
Therefore we will magnify the part of the Thuring board where this part of the timer is located.
Let us first install the HEF 4521BT on the board. Watch out how you mount it!
Next will will solder the NYMPH quartz. Because SARONIX came up with the idea of wrapping the quartz in a plastic sleeve, the quartz can be mounted flat on the board without risk of short circuit. Pretty smart. That is the way you beat the competitors.
And all there is left to do is to solder the 1M resistance and the 2 capacitors (33 and 27 pF)
And we are done! Let us now compare this with the Togo timer!
Everything looks right… Except for this variable capacitor. Remember the CIA report?
As I stated before, I suspect that Lumpert realized that the timer was inaccurate. So, he decided to “pull” the frequency by tuning the “load capacitance” applied to the quartz, thus the use of a variable capacitor. (The theory is explained in reference 1.)
But of course, the Thuring boards he had already designed and ordered had NOT been designed for this. The variable capacitor is simply too big to fit at the original spot. And all Lumpert can do is to mount the variable capacitor in a way that fits the board. And this is his solution.
You may also notice the two chip resistors ( R2 and R3 on the CIA diagram) added by bending up leads on the IC HEF 4521BT (pin 3 and 5). These were not planned by Lumpert. They are NOT necessary but they are useful as they are recommended for low power operation. And finally, take note of the two jumper wire corrections (on the left of the IC HEF 4521BT).
This is it. We are now – almost – ready to listen to whatever Lumpert has to say about the Togo timer!
1. Quartz Crystal (Design Note)